Microphone



April 14,- 1925. 1,533,675 A. THOMAS I MICROPHONE Filed Aug 11, 1920 M/g/bl:

' Albert Thomas,

His Attorney.

Patented Apr. 14, 1925.

ALBERT THOMAS, F PARIS, FRANCE.

MICROPHONE.

Application filed August 11, 1920. Serial No. 402,778.

To all whom it may concern:

.Be it known that I. ALBERT THOMAS, a citizen of the French Republic, residing at Paris, France, have invented certain new and useful Improvements in Microphones, of which the following is a specification.

This invention relates to instruments which utilize loose or imperfect electrical contacts and has for its object the protection of such contacts from injury or deterioration when in use. This I accomplish by suitably arranging a. discharge resistance in shunt to the contacts of the instrument.

Referring to the drawing, Fig. 1 is a front plan view of a microphone embodying my invention, with the vibrating diaphragm, attaching ring and gasket removed; Fig. 2 is a section taken on the line 2-2 .of Fig. 1; and Fig. 3 is a diagrammatic view of the circuit connections.

The microphone comprises a cup 10,,t0 the back of which is secured a metallic plate 11 by means of screws 12. Screws 12 as well as plate 11 are insulated from the cup and one of these screws serves to form an electrical connection between the microphone terminal 13 and the plate 11. Cup 10 is formed with a central opening 14 and secured within this opening is a bushing 15 of insulating material. This bushing is closed at the rear by a conducting plate 16, which closely fits within the bushing 15, and is in contact with the metallic plate 11. The forward end of the bushing is closed by a conducting plate 17 which serves as the vibrating diaphragm of the microphone and is secured between the outer rim of the cup 10 and the inwardly turned flange 18 of the ring 19. Interposed within the flange 18 and the diaphragm is a suitable packing 20. The diaphragm 17 is connected to microphone terminal 21 through cup 10 and screw 22. Bushing 15 contains granular carbon or other conducting material 23 which lies in contact with plate 16 and diaphragm 17. The material 23 forms with the plate 16 and diaphragm 17 what I term loose or imperfeet electrical contacts.

: Connected between the microphone terminals 13 and 21 and bridging the operating contacts of the microphone is a coil 24 which in the present instance is located within the cup 10 and surrounds the bushing 15. The

windings of the coil 24- are held within an annular casing 25 which, as may be seen in Fig. 2,is U-shaped provided with lips the rear side of the the metal toward the secured to the cup 10 by the in cross-section and is 26 formed by slitting casing 25 and bending center. These lips are screws 12.

Fig. 3 shows one manner of connecting my transmitter to the line, namely by means of a transformer 30 the primary of WlllClllS connected in a circuit which includes the transmitter and a source of. current 31.

From the above description it will be microphone.

lVhile I have shown my invention as applicable to a microphone, it is to be understood that it is in no wise limited thereto but may be applicable generally to instruments which utilize partial trical contacts.

, loose or imperfect elec- What I claim as new and desire to secure by Letters Patent of the United States, is

1. A microphone t member adapted to ransmitter comprising a be vibrated by sound waves, a body of loose conducting material engaged by said member rality of contacts,

and forming a pluand means whereby said contacts are protected from injury, said means comprising a discharge resistance con nected to bridge said contacts.

2. A microphone t diaphragm,

ransmitter comprising a an 'annular member adjacent said diaphragm contalnmg loose conducting material forming a plurality of contacts actuated by said diaphragm, and means for protectlng said contacts from excessive current comprising a r esistance coil connected in shunt relation to said material and arranged to surround said annular member and lie adjacent said diaphragm.

3. The combination with a cup provided with a central opening,

within said opening of a bushing fitted a conducting plate secured to said cup and covering the rear end of said bushing, a conducting diaphragm secured against the rim of the cup and closing the forward end of said bushing, granular conducting material located Within said bushing and in electrical connection with said plate and diaphragm, a coil located Within said cup and surrounding said bushing, and means connecting one terminal of the coil to said plate and the other to said 10 diaphragm.

In Witness whereof, I have hereunto set my hand this 23d day of July, 1920.

ALBERT THOMAS. 

